A Bradford-born policing chief has spoken of the “meticulous” and “very, very difficult” investigation into the UK’s most prolific serial rapist.

Reynhard Sinaga, aged 36, has been jailed for life after drugging at least 48 men and filming himself sexually violating them while they were unconscious in his Manchester city centre apartment.

Greater Manchester’s Assistant Chief Constable Mabs Hussain, who began his policing career as a uniformed PC in Bradford, said: "My first appeal would be to anybody who may think they have had contact with Reynhard Sinaga, the circumstances as reported have brought back some memories and they suspect they have been on a night out and met somebody like Reynhard Sinaga to contact the police.

"We have specialist officers waiting, we have a helpline where the numbers are available and we are working with specialist victim support services including St Mary's Sexual Assault Referral Centre, Survivors Manchester and Victims' Services.

"At the forefront of this investigation and our primary objective throughout has been to provide the support to the victims and I would encourage them to come forward. We have the specialist services to provide that support."

Mr Hussain, who grew up in Girlington and spent over two decades with West Yorkshire Police, added: "We believe Reynhard Sinaga is the UK's most prolific rapist and the reason I say that is because on the information and evidence we suspect there are in total 190 victims approximately who have been involved.

"We can't give you a definitive figure for obvious reasons. Forty-eight of them have supported a criminal prosecution.

"Of that 190 there are approximately 70 that we are still yet to identify and the reason we have still yet to identify them is despite our best efforts, and the investigation team working tirelessly to piece together the information, we have been unable to identify who each individual is to speak to them. There is still some work for us to do."

He said officers had undertaken a "very very difficult" investigation with almost three terabytes of data pored over - the equivalent of watching 1,500 DVD films.

Mr Hussain explained: "One of my officers described it as like putting together a jigsaw without the picture because it was not apparent which parts were from which offence.

"Each visit to each of these victims has had to be carefully and meticulously planned, and their welfare and wellbeing was at the forefront of our mind in dealing with the victims."

He said Sinaga was a "depraved sexual predator" who had taken advantage of trusting young men, but he added: "I think we need to concentrate less on Reynhard Sinaga as an individual and focus much more on each individual victim who has either supported the prosecution or provided evidence and information.

"I cannot begin to imagine what they have had to endure, what they have had to go through and what they are still living with today."